The present invention concerns a filter for a pipe. More particularly, but not exclusively, this invention concerns a filter comprising an attachment portion for attaching to the pipe, and a filter surface for presentation to and filtering of an oncoming flow of the pipe. The invention also concerns a pipe for transporting an oncoming flow, wherein the pipe is provided with a filter surface across the cross-sectional area of the pipe and an aircraft with such a filter or pipe. The invention also concerns a method of filtering an oncoming flow of a pipe.
An aircraft fuel system, for example, has a number of flow devices that use suction pressure to induce flow out of a fuel tank and into a pipe. These flow devices often contain small diameter pipes and nozzles that can become blocked by debris induced into the system from the fuel tanks. Current pipe filters comprise a mesh screen over the pipe inlet. The mesh screen can be either flat across the pipe inlet or can be slightly rounded to form a convex end on the pipe inlet.
These types of mesh screen can cause a variety of problems. For example, the mesh screen inevitably blocks some of the pipe inlet area and so causes a pressure drop across the pipe inlet and a loss of efficiency. Furthermore, partial blockage of the filter results in a further pressure drop across the filter and further loss of efficiency. Also, a debris particle that is larger than the pipe inlet diameter can be held against the mesh screen by suction pressure and can completely block the inlet. In addition, the mesh screens are susceptible to ice formation, especially where the pipe inlet is located in an area of relatively high water concentration, for example in the inlet to a water scavenge jet pump. Ice formation can also lead to a partial or full blockage of the pipe. In order to prevent ice formation, larger-holed mesh screens can be used but these can cause larger debris particles to pass through the filter and can cause blockage in the systems.
Blockages are often only found when a problem occurs and are very difficult and time consuming to discover. Furthermore, cleaning the blockages, for example for filters in aircraft fuel tank systems, requires entry into the aircraft fuel tank. This is expensive and raises several health and safety concerns.
The present invention seeks to mitigate the above-mentioned problems. Alternatively or additionally, the present invention seeks to provide an improved filter or pipe or an improved method of filtering an oncoming flow of a pipe.